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MOR‐1‐immunoreactive neurons in the dorsal horn of the rat spinal cord: evidence for nonsynaptic innervation by substance P‐containing primary afferents and for selective activation by noxious thermal stimuli by R. C. Spike; Z. Puskár; H. Sakamoto; W. Stewart; C. Watt; A. J. Todd is a Neuroscience article available to read on EtoBox.

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## Abstract A direct action of μ‐opioid agonists on neurons in the spinal dorsal horn is thought to contribute to opiate‐induced analgesia. In this study we have investigated neurons that express the μ‐opioid receptor MOR‐1 in rat spinal cord to provide further evidence about their role in nociceptive processing. MOR‐1‐immunoreactive cells were largely restricted to lamina II, where they comprised approximately 10% of the neuronal population. The cells received few contacts from nonpeptidergic unmyelinated afferents, but many from substance P‐containing afferents. However, electron microscopy revealed that most of these contacts were not associated with synapses. None of the MOR‐1 cells in lamina II expressed the neurokinin 1 receptor; however, the μ‐selective opioid peptide endomorphin‐2 was present in the majority (62–82%) of substance P axons that contacted them. Noxious thermal stimulation of the foot induced c‐Fos expression in approximately 15% of MOR‐1 cells in the medial third of the ipsilateral dorsal horn at mid‐lumbar level. However, following pinching of the foot or intraplantar injection of formalin very few MOR‐1 cells expressed c‐Fos, and for intraplantar formalin in

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Author

R. C. Spike; Z. Puskár; H. Sakamoto; W. Stewart; C. Watt; A. J. Todd

Publisher

John Wiley and Sons; Wiley (Blackwell Publishing); Blackwell Publishing Inc.; Wiley (ISSN 0953-816X)

Published

2002

Language

EN

Field

Neuroscience (Life Sciences)